In disc drives, the positioning of a read/write head relative to a track that is being accessed is subject to non-repeatable runout errors. One component of the non-repeatable runout error is due to the instability of airflow patterns that are generated by the rotating disc. Unstable airflow impacts on actuator arms and head gimbal assemblies (HGAs) that position the read/write heads over the discs. The unstable airflow excites various mechanical vibration modes that cause arm/HGA off-track motion which results in non-repeatable runout errors. In particular, arm/HGA sway and arm/HGA torsion modes are typically excited. As areal density of disc drives increase, and the speed of rotation of the discs increases in new designs, the problems with non-repeatable runout due to unstable airflow patterns becomes worse.
A method and apparatus are needed that will reduce non-repeatable runout errors in disc drives with higher areal densities and higher speeds. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.